Going from 80 gallons to about 270 gallons. Will be a peninsula as well in same spot in the house.How big is the new tank?
Yes agree absolutely an issue if you don’t control humidity. This is going on probably 8 or so years with a basement sump/ tanks. I have always controlled humidity through one having central forces air which circulates air in basement through the heating cooling system and 2 from use of dehumidifiers. Humidity in the basement is kept under 50% and have never had issues with rusting. Definately something that needs to be managed in any set up thoughhaving a sump in the basement is nice and could make everything easy for the reef keeping hobby for sure.
Just a tip, You might want to cover up anything that has metal otherwise they can get rusted over times from the salt moisture. To name a few, heater furnace, jack post, gas pipes, pipe column, breaker box...etc.